1. Field of the Invention
The present invention relates to a method and an apparatus for the compressing and coding of image data representative of a color image, and a digital camera including the same. More particularly, the present invention relates to an image processing method for compressing and coding image data derived from, e.g., a shot in either one of a color mode and a monochrome mode and then recording them in a recording medium, an apparatus therefor, and a digital camera including the same.
2. Description of the Background Art
A digital still camera, for example, belongs to a family of image processing apparatuses of the type using a CCD (Charge Coupled Device) image sensor or similar solid imaging device and a semiconductor memory, magnetic disk or similar image data recording medium. The digital still camera transforms a color image signal representative of a scene picked up by the image sensor to a digital signal, compresses and codes the transformed image data by bidimensional orthogonal transform or similar transform system, and records the coded image data in the recording medium.
In the digital still camera, color image data produced by, e.g., the block interleaving of luminance data and chrominance data are subjected to bidimensional orthogonal transform and coding. The resulting coded data are compressed and coded to turn out, e.g., a preselected amount of codes and then written to a desired recording medium. For compression coding, use is made of, e.g., a JPEG (Joint Photographic Coding Experts Group) system based on "ISO/IEC DIS 10918-1". The processed image data can not only be printed, but be further processed by a general-purpose personal computer for any desired application.
However, the conventional digital still camera has some problems left unsolved, as follows. The camera has customarily been constructed principally to shoot a natural image or similar subject and output a corresponding color image. The camera therefore cannot output, e.g., line images, characters or monotone or similar monochrome images without resorting to special arrangements. It follows that to record monochrome image data in a recording medium, the recording format or even the construction of the entire camera must be substantially changed.
To record monochrome image data in a recording medium, the CCD imaging sensor or similar imaging device may be implemented by an exclusive imaging device for monochrome. Alternatively, in a monochrome mode, an exclusive color filter for color images may be removed from the front of the imaging device. Further, an exclusive signal processing circuit for monochrome may be additionally built in the camera in order to generate only the luminance component of an image signal and subject it to compression coding.
However, adding an exclusive imaging unit or an exclusive signal processing circuit for monochrome is not practicable without reconstructing the entire camera. Also, image data output by a special compression system dealing only with the luminance component of an image signal cannot be reproduced by a conventional reproducing system. Moreover, a special black-and-white mode must be prepared even for the format for recording the image data. Therefore, the camera, like an exclusive monochrome camera, cannot be compatible with conventional cameras or image data reproducing apparatuses, i.e., it does not allow image data output therefrom to be reproduced by the conventional apparatuses.
Japanese patent laid-open publication No. 107904/1990 assigned to the same assignee as the present application teaches a digital still camera capable of recording, when a black-and-white mode is selected, only original image data relating to a luminance component and subjected to compression coding in both of the luminance component area and chrominance component area of a memory cartridge. This camera, however, does not give full consideration to the compatibility of recorded data. For example, it is difficult with this type of camera to decode recorded data within the range of a standardized basic system and reproduce an image.
As stated above, it is necessary to substantially change the construction of a conventional digital still camera of the type outputting color image data and recording them in a recording medium. This increases the cost and makes it difficult to implement a simple and convenient digital still camera capable of outputting not only a color image but also a monochrome image, as desired. For example, it is difficult to realize a simple and convenient digital still camera adaptive to both of a color image and a monochrome image and outputting image data while insuring compatibility therebetween.